The functionality and service life of sensors can be negatively affected by certain operating states and environmental influences. For example, the output signal of a hot film air-mass meter can be corrupted briefly or permanently by an impermissibly high level of contamination caused by the carry-in of harmful media such as oil, water, particles or salt crystals during vehicle operation. With some types of sensors, the operation of the sensors itself even promotes the depositing of harmful media.
Sensors already exist today that are deactivated in some operating states, e.g., during engine after run, that is, for a certain length of time after vehicle operation has ended, during which time some systems are still supplied with voltage. This takes place without any additional switches, e.g., by the driver switching off the voltage via terminal 15 of the vehicle. When the driver switches off the voltage via terminal 15, hot film air-mass meters are also deactivated.
The problem of a measuring error potentially occurring when a hot film air-mass meter becomes contaminated is known and necessitates that countermeasures be taken.
It is therefore provided in DE 101 63 751 A1, for example, that the output signal of a hot film air-mass meter be changed if contamination occurs or that a different signal be accessed, to prevent measuring errors. A short-term depositing of media on a sensor is detected during vehicle operation, e.g., via a software function that evaluates certain sensor signals or default signals. A plausibility check of this type or substitution of the air-mass sensor signal carried out when a signal disruption occurs ensures that the internal combustion engine can continue to be operated reliably even if the sensor is contaminated. The software function used to detect the media carry-in includes, e.g., a calculation of the difference between two signal gradients. In DE 101 63 751 A1, therefore, a default signal is accessed when the media carry-in is detected. The publication does not mention the sensor being deactivated if contamination occurs, however.
From DE 32 31 142 A1 it is known to use a sensor that measures the water level with a water display device for fuel water separators. This sensor is deactivated as soon as the water reaches the sensor tip. Corrosion of the sensor tip is thereby prevented, which extends the service life and improves the usability of the sensor.